Blazar Times - No. 44 - June 2002
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 44 - June 2002 Editor: Travis A. Rector (blazar@nrao.edu)

TABLE OF CONTENTS

Journal Abstracts 1

Abstract Guidelines 4

Journal Abstracts

Optical Variability of Gamma-Ray Loud Blazars

A.C. Gupta1,2, U.C. Joshi1  and J.H. Fan3,4

1 Astronomy and Astrophysics Division, Physical Research Laboratory, Navarangpura, Ahmedabad - 380 009, India
2 Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad - 211 019, India
3 Center for Astrophysics, Guangzhou University, Guangzhou 510400, China
4 Chinese Academy of Sciences-Peking University Joint Beijing Astrophysical Center (CAS-PKU.BAC), Beijing, China

Blazars display flux variability on diverse timescales ranging from minutes to months. In our blazar monitoring project carried out on the 1.2 meter telescope at Gurushikhar, Mount Abu, India. We selected some g-ray loud blazars to study the variability over both the short and the long time scales. In this paper we have reported results based on photometric monitoring on 8 nights during the observing run in the first half of the year 2000 for 5 blazars: S5 0716+714, OJ 287, S4 0954+658, Mrk 421 and PKS 2155-304 in B and R passbands. Microvariability and rapid variability has been observed in these sources suggesting that variability is a common property in these objects.

Accepted by Ap & SS

For preprints contact: agupta@mri.ernet.in

The WEBT BL Lac Campaign 2000

M. Villata1, C. M. Raiteri1, O. M. Kurtanidze2,3,4, M. G. Nikolashvili2, M. A. Ibrahimov5,6, I. E. Papadakis7,8, K. Tsinganos7, K. Sadakane9, N. Okada9, L. O. Takalo10, A. Sillanpää10, G. Tosti11, S. Ciprini11, A. Frasca12, E. Marilli12, R. M. Robb13, J. C. Noble14, S. G. Jorstad14,15, V. A. Hagen-Thorn15,16, V. M. Larionov15,16, R. Nesci17, M. Maesano17, R. D. Schwartz18, J. Basler18, P. W. Gorham19, H. Iwamatsu20, T. Kato20, C. Pullen21, E. Benítez22, J. A. de Diego22, M. Moilanen23, A. Oksanen23, D. Rodriguez24, A. C. Sadun25, M. Kelly25, M. T. Carini26, H. R. Miller27, S. Catalano12, D. Dultzin-Hacyan22, J. H. Fan28, R. Ishioka20, H. Karttunen10, P. Keinänen10, N. A. Kudryavtseva15, M. Lainela10, L. Lanteri1, E. G. Larionova15, K. Matsumoto20, J. R. Mattox29, F. Montagni17, G. Nucciarelli11, L. Ostorero30, J. Papamastorakis7,8, M. Pasanen10, G. Sobrito1  and M. Uemura20

1 Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Via Osservatorio 20, 10025 Pino Torinese (TO), Italy
2 Abastumani Observatory, 383762 Abastumani, Georgia
3 Astrophysikalisches Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
4 Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, 69117 Heidelberg, Germany
5 Ulugh Beg Astronomical Institute, Academy of Sciences of Uzbekistan, 33 Astronomical Str., Tashkent 700052, Uzbekistan
6 Isaac Newton Institute of Chile, Uzbekistan Branch
7 Physics Department, University of Crete, 710 03 Heraklion, Crete, Greece
8 IESL, Foundation for Research and Technology-Hellas, 711 10 Heraklion, Crete, Greece
9 Astronomical Institute, Osaka Kyoiku University, Kashiwara-shi, Osaka, 582-8582 Japan
10 Tuorla Observatory, 21500 Piikkiö, Finland
11 Osservatorio Astronomico, Università di Perugia, Via B. Bonfigli, 06126 Perugia, Italy
12 Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
13 Department of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada
14 Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave., Boston, MA 02215, USA
15 Astronomical Institute, St.-Petersburg State University, Bibliotechnaya Pl. 2, Petrodvoretz, 198504 St.-Petersburg, Russia
16 Isaac Newton Institute of Chile, St.-Petersburg Branch
17 Dipartimento di Fisica, Università La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy
18 Department of Physics and Astronomy, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA
19 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
20 Department of Astronomy, Faculty of Science, Kyoto University, Kyoto, Japan
21 Clarke and Coyote Astrophysical Observatory, PO Box 930, Wilton, CA 95693, USA
22 Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México DF, Mexico
23 Nyrölä Observatory, Jyväskylän Sirius ry, Kyllikinkatu 1, 40950 Jyväskylä, Finland
24 Guadarrama Observatory, C/ San Pablo 5, Villalba 28409, Madrid, Spain
25 Department of Physics, University of Colorado at Denver, PO Box 173364, Denver, CO 80217-3364, USA
26 Department of Physics and Astronomy, Western Kentucky University, 1 Big Red Way, Bowling Green, KY 42104, USA
27 Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA
28 Center for Astrophysics, Guangzhou University, Guangzhou 510400, China
29 Department of Chemistry, Physics, & Astronomy, Francis Marion University, PO Box 100547, Florence, SC 29501-0547, USA
30 Dipartimento di Fisica Generale, Università di Torino, Via P. Giuria 1, 10125 Torino, Italy

We present UBVRI light curves of BL Lacertae from May 2000 to January 2001, obtained by 24 telescopes in 11 countries. More than 15000 observations were performed in that period, which was the extension of the Whole Earth Blazar Telescope (WEBT) campaign originally planned for July-August 2000. The exceptional sampling reached allows one to follow the flux behaviour in fine details. Two different phases can be distinguished in the light curves: a first, relatively low-brightness phase is followed by an outburst phase, after a more than 1 mag brightening in a couple of weeks. Both the time duration (about 100 d) and the variation amplitude (roughly 0.9 mag) are similar in the two phases. Rapid flux oscillations are present all the time, involving variations up to a few tenths of mag on hour time scales, and witnessing an intense intraday activity of this source. In particular, a half-mag brightness decrease in about 7 h was detected on August 8-9, 2000, immediately followed by a ~ 0.4  mag brightening in 1.7 h. Colour indexes have been derived by coupling the highest precision B and R data taken by the same instrument within 20 min and after subtracting the host galaxy contribution from the fluxes. The 620 indexes obtained show that the optical spectrum is weakly sensitive to the long-term trend, while it strictly follows the short-term flux behaviour, becoming bluer when the brightness increases. Thus, spectral changes are not related to the host galaxy contribution, but they are an intrinsic feature of fast flares. We suggest that the achromatic mechanism causing the long-term flux base-level modulation can be envisaged in a variation of the relativistic Doppler beaming factor, and that this variation is likely due to a change of the viewing angle. Discrete correlation function (DCF) analysis reveals the existence of a characteristic time scale of variability of ~ 7 h in the light curve of the core WEBT campaign, while no measurable time delay between variations in the B and R bands is found.

Accepted by A&A

For preprints contact: villata@to.astro.it

For preprints via ftp or WWW: http://www.to.astro.it/blazars/webt/bl00.ps.gz

Abstract Guidelines

Abstracts for ``The Blazar Times" are solicited for papers that have been recently accepted for publication by a refereed journal, and for recent Ph.D. theses. Please do not submit an abstract before it has been accepted, nor after it is published. Abstracts from papers which are not refereed (e.g., conference proceedings) are not accepted.

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